A supercalender normally comprises a stack of rolls consisting of a number of rolls fitted one above the other, in which stack, between the upper roll and the lower roll in the calender, there are a number of intermediate rolls, which are alternatingly chilled rolls and soft-faced rolls. Earlier, as soft-faced rolls, almost exclusively so-called fibre rolls were used, which consisted of disks or rings of fibrous material fitted on the roll axle and pressed together axially by means of end pieces and end nuts so that the soft face of the roll consisted of said fibre disks. It was one drawback of such fibre rolls that the deflections and rigidities of said fibre rolls differed quite substantially from corresponding properties of the chilled rolls, because the frame of the fibre rolls is quite slender as compared with the chilled rolls. As second significant drawback was relatively rapid wear of the fibre rolls.
Development of rolls and roll coatings made it possible, in supercalenders, in stead of fibre rolls, to employ rolls provided with elastic coating, in particular with a polymer coating, as soft rolls. In such rolls, the thickness of the coating in relation to the roll diameter is quite little, in which case the roll frame can be made quite rigid. Thus, in particular when rolls with polymer faces are employed, the rolls can be constructed so that the rigidities and deflections of all of the intermediate rolls in the calender are substantially equal, or at least the differences in these properties from roll to roll are quite little. It is a second improvement in polymer-coated rolls, as compared with fibre rolls, that their service life is considerably longer, i.e. the intervals of replacement of rolls can be made considerably longer.
In conventional rolls with polymer coatings, a significant problem, however, consists of the relatively high weight of the rolls as compared with fibre rolls. Thus, these polymer-coated rolls of novel type cannot be used as such in renewals and modernizations of existing calenders in which fibre rolls were used as soft-faced rolls earlier. This comes simply from the fact that, in a calender which was originally designed so that fibre rolls are employed as intermediate rolls, the mechanical strength of the spindles and spindle nuts on whose support the rolls are suspended does not endure the increased weight resulting from the polymer-faced rolls. Thus, in modernizations of supercalenders, if it is desirable to employ polymer-coated rolls of new type, considerable changes and renewals must be carried out in the frame constructions of the calender and in the means of suspension of the rolls. Thus, it is an aim to be able to reduce the weight of the polymer-faced rolls employed in supercalenders substantially in order that such rolls, whose other properties are better than those of fibre rolls, could be used simply also in modernizations of supercalenders.
With respect to the prior art, reference is made to the U.S. Pat. No. 3,711,913, to the DE Patent 195 11 595 (corresponding to U.S. Pat. No. 5,766,120), to the published DE Patent Application 195 33 823 (corresponding to U.S. Pat. No. 5,759,141), and to the published EP Patent Application 735,287 (also corresponding to U.S. Pat. No. 5,766,120).
In said U.S. Patent, a method is described for conditioning of a fibre roll, in which method a worn or damaged fibre roll is machined to a measure smaller than its original diameter, after which a coating of a synthetic plastic material is fitted onto the roll, i.e. directly onto the fibre disks. With this procedure, the roll can be made suitable for a certain purpose of use, but the properties of a roll manufactured or conditioned in compliance with said method do not correspond to what is required from a modern polymer-faced calender roll. First, the rigidity of the roll is considerably lower than the rigidity of a tubular polymer roll, and further, since the coating has been fitted directly onto the fibre disks, the properties of resilience of the roll differ considerably from what is expected, for example, from a modern tubular polymer roll.
In the DE and EP publications referred to above, polymer-faced calender rolls are described which have been formed so that, in the roll, the axle of an existing fibre roll is used so that, onto the axle, in place of the filler material of the fibre roll, for example, disks made of aluminum cell material are fitted, in which disks at least a part of the walls of the cells are perpendicular to the roll axle. Then, onto these disks, an elastic polymer coating has been fitted. The roll formed in this way has quite good properties, in particular because the weight of the roll has become so low that it can be utilized easily in renewals of supercalenders, because the difference in weight of the roll as compared with a fibre roll is very little. It is a significant drawback of these rolls that, according to a first embodiment, the roll is manufactured by pressing loose disks between locking flanges, as is the case in traditional paper rolls, in which case it is very difficult to provide the desired rigidity. The rigidity is determined in accordance with the pre-stress of the axle and with the compression strength of the disks, as is the case in traditional paper rolls. In a second embodiment desribed in the cited prior-art publications, the support construction is composed of a plate of cellular construction which is wound as layers onto the axle. In the embodiment described in the publications, this procedure requires formation of joints in the longitudinal direction of the roll and bending of large plate-like pieces into correct shape, which requires high precision and care of manufacture. A further drawback is the high cost, which comes, besides from the above reasons, also from the technique of manufacture that has been used, which requires casting and machining of the disks. Also, depending on the purpose of use and on the diameter of the roll, the disks must always be designed anew, and a number of different cast models must be prepared for different rolls. In said publications, as a further alternative embodiment, forming of disks has been suggested out of a material that contains reinforcement fibres, such as epoxy reinforced with fibreglass, carbon fibres, aramide fibres, or equivalent. Such solutions are, of course, usable in themselves, and they provide a roll of quite low-weight construction, but the problem is an even higher cost.
The object of the present invention is to provide a novel method for manufacture of a calender roll provided with an elastic coating as well as a calender roll manufactured in accordance with the method, which method and roll do not involve the drawbacks involved in the prior art and by means of which method and roll, further, a significant improvement is achieved over the prior art. In view of achieving the objectives of the invention, the method in accordance with the invention is mainly characterized in that the filler material is made of a continuous profile band, which is wound onto the axle as the desired number of windings in order to produce the desired roll diameter, in which connection an elastic coating is formed onto the cylindrical outer face of the filler material.